1. Field of the Invention
This invention relates to thermally expandable solid structures having hollow sealed cores containing an expandable material which may expand at the same or different rates on opposite sides of the structure depending on design geometry. The rings are useful as seals or gaskets and other configuration may be used as passive regulator devices or shut-off devices and as inserts in pipes and tubes. They are especially useful in heated environments and especially at high temperatures.
2. Background and Prior Art
Gaskets are used to fill spaces between surfaces. As such, they must be flexible and expand or shrink under the same conditions as the mated surfaces. In some cases a filler in an essentially round or oval cross-section of flexible material is used. Most commonly the filler is air such as in the gasketing around an exterior passage door of a building.
U.S. Pat. No. 5,294,133 to Dutta discloses an o-ring useful in a cylinder bore which is an elastomer filled with a fluid such as a mixture of water and glycol to maintain a seal at low temperatures.
Japanese Kokai Showa 61-096264 discloses a metal gasket in the form of a spiral lock washer that is a thin-walled tube filled with a metal having a low melting point which expands upon melting. The gasket is intended for high temperature uses.
The disposal of radioactive waste material is an acute problem world-wide that presents technical and political challenges. Not only do the wastes—especially actinides—have long half-lives and high energy emissions, they often appear in chemical forms which are unfriendly to mammals and materials. One approach to the isolation of radioactive waste has been incorporation into glass logs. U.S. Pat. No. 4,797,232 to Aubert, U.S. Pat. No. 5,461,185 to Forsberg et al., and U.S. Pat. No. 5,494,863 are representative of patents directed to methods for incorporating radioactive waste into glass logs.
Thermally actuated valves have been based upon convection (U.S. Pat. No. 6,584,940), expansion of gas behind a diaphragm (U.S. Pat. No. 6,540,190) or employment of a bimetallic element to control a low-mass flap (U.S. Pat. No. 4,555,981). Cut-off (or turn-on) valves for fire protection typically employ fusible links in accordance with the requirements of 29 CFR 1910.1016(b)(4)(iv)(c)(OSHA) and National Fire Protection Association standards. Reliable alternatives that do not require exposed components are desirable.